Muffle



1% 31, 1193. H. H. HARRIS 2914159257 MUFFLE- Filed Aug. 17, 193'? rsom sINVENTOR Henry H. Harm's I ATTORNEYS Patented Jan. 31, 1939 UNITEDSTATES PATET FFlC Application August 1'7,

22 Claims.

My invention relates to mufiles used in heattreating furnaces, andparticularly to a muffle or like container suspended or otherwisedisposed within a furnace, the articles to be heat-treated being placedwithin the muffle or passed therethrough for treatment.

Conventional mufiles are made of cast metal alloy, which renders themboth heavy and ex pensive. since weight is a cost factor. It is the mainobject of my invention to make a light and relatively cheap mufiie, andI accomplish this by making the muffle partly of cast alloy metal andpartly of sheet alloy metal, preferably nickelchromium-iron alloy metalor steel adapted to resist heat and corrosion.

Sheet metal heats up and cools down much more quickly than does castmetal, with possible development of strains at and near connections ascommonly made between the cast and sheet parts. It is a further objectof my invention to provide a muffle of cast and sheet metal, the partsof which are so connected that they will heat up and cool down at afairly uniform rate, especially at and near the regions where cast andsheet parts are interconnected.

The use of cast muilles involves a long heating up period before theheat is transmitted to the mufiie contents. Mufile walls of sheet metalheat up and cool off at a more rapid rate, and it is a further object ofmy invention to reduce the time required for muffle operation, and Iaccomplish this by making the greater part of the muffle area of sheetmetal, and using only a relatively small proportion of the cast metalwhich is needed to give the muffle strength and rigidity.

Further objects of my invention will in part be obvious and in partspecifically pointed out hereinbelow in connection with the followingdescription of an illustrative embodiment.

40 In the drawing annexed hereto and made a part hereof,

Fig. 1 is a transverse section through a conventional heat-treatingfurnace, and showing, also in section, one form of muille constructedaccording to and embodying my invention, suspended therein;

Fig. 2 is a side elevation of the muffle, partly broken away and partlyin section on the line 22 of Fig. 3; and

Fig. 3 is a plan view of the muffle, with parts broken away.

Furnace it) comprises side walls l2, l2 and arched roof Hi, definingchamber l 5 within which muflle i8 is suspended by means of chains 22,22, secured to eyebars 24, 24, anchored in and 1937, Serial No. 159,481

through roof It by means of nuts 26, 29. Eyebars 24, 24 are preferablyangled with respect to each other to distribute the weight load overroof l4 and better support the mufile weight.

Rails 25, 25 are provided on elevated platforms, 29, 29, within thefurnace and extending lengthwise thereof, which rails bear at an angleagainst the underside of muffle l8 and support part of the weightthereof. Roller rails may be used if desired. I support most of themuffle weight preferably from above, and I am thus enabled to utilizethe weight of the muffle and of its contents for holding the sheetportions thereof in a state of extension or semi-rigidity and to therebydispense with need for braces, stiffeners, and the like, for the sheetmetal portions. The drawing illustrates one Way of suspending a mufllewithin the furnace chamber, but this can be done in various ways.

The wall members of mufile l8 comprise cast portions 28, 28, and 29, 29,and sheet portions 39, 32, 32, and 3'! of heat and corrosion resistingalloy metal. Cast portions 28, 28 form the upper corners of the muffleand are provided with upwardly extending ears 33, 34 to which thesuspending chains 22, 22 are secured. The upper corner bars 28, 28 arepreferably identical, and are provided with a central depression 3i withthe inner edges 36 curving down and inwardly and the outer edges 38curving out and decidedly in a reverse direction from the depressedmiddle. In cross-section the curvature near the edges 36 and 38 of bars28 is almost semi-circular. Sheet 39 is welded on to the upper convexsurfaces of the inner parts 35, 3B, of bars 28, 28, to form the top wallof the muffle ill. The welding is preferably disposed at and near theedge of sheet num-- ber 39 and a wide overlap between the sheet metaland cast metal is provided as hereinafter referred to.

Cast portions 29, 29, form the lower corners of the muille. The lowercorner bars 29 are preferably identical and have a flat central trackportion 58, with the inner and outer edges 99, 69 and l9, 79respectively of bars 29 curving away therefrom in opposite directions.In cross-section, the curvature near the edges of corner bars 29, 29 isshallower than the curvature of the upper corner bars 22, 2B.

A pair of sheets 32, 32 are provided to form the side Walls of themuffle. The upper edge 39, 33 of sheets 32, 32 is welded to the convexouter surface of the outer edge portions 38, 38, of the upper cornerbars 28, 28, and the lower edge 35, of sheet 32, 32, is Welded to theconvex outer surface of inner edge 60, 60, of lower corner bars 29, asseen in Fig. 1. A fourth sheet 3! is provided to form the bottom of themuffle. In connecting bottom sheet 37 to the lower corner bars 29, theedges 62 of sheet 31 are superposed upon and lapped over the convexupper surfaces of the inner edge portions 10, 10 of corner bars 29, andthe welding is done at the extreme margins of edges 62 of sheet 31.

The floor 40 in the muflie is supported by the lower corner bars 29, 29.Thus corner bars 29 serve not only as a means of attachment for thesheet metal parts but also for supporting the floor upon which the workis supported in turn. In forming the floor 40 a plurality of cross-beams42 are disposed transversely within the muffle which serve as a supportfor work supporting tracks 44.

To help support the mufiie weight and keep same from swinging within thefurnace, and putting extra strain on the suspending mechanism, as mayoccur in loading and unloading, I provide tracks 25, 25, mounted onplatforms 26, 26, which bear against the underside of the flat centraltrack portion 58 of corners 29, 29. The height of tracks 25 may beadjusted to compensate for variation of muffle weight, according to thework therein. The weight of the floor members and the contents of themufile serve to put sheets 32, 32 under tension, and this tension istaken up and absorbed by the curved surface connections terminating atwelds 52, 53. Thus the sheet wall parts 32 remain substantially rigidwithout reenforcing or bracing. Sheet 36, comprising the muflle roof orhood, and sheet 3'! comprising the muflle bottom are under no particulartension other than their own dead weight, and may permissibly sagcentrally, as shown.

The connections between cast and sheet members comprise broad overlapsas shown, and the welded connections are made at and near the edges ofthe sheet portions with the principal part of the overlap consisting ofthe sheet resting freely upon and in contact with a convex surfaced partof cast metal. The cast metal edges as 49 are turned in or away so as toface away from the sheet metal and not to contact the sheet, thusavoiding any injury to sheets from sharp edges of cast metal. Themarginal parts of the sheets thus heat up and cool off with the roundedcast metal with which they are in contact. Thus the welded jointsbetween the cast metal and sheet metal are relieved from strains causedby uneven heating and cooling rates of thin sheet metal and thicker castmetal as will be readily understood. When an extra-long muffle isdesired, I weld together end to end a plurality of sections, as shown at56.

My improved muffle is much lighter and cheaper than mufiles madeentirely of cast alloy, for example. Increased efficiency is secured bymaterially reducing the time required for the heat treatment operation,the sheet wall portions heating up rapidly and transmitting heat rapidlyto the articles being treated. If desired, brace bars 82 may be weldedor otherwise secured to the muffle roof, overlying sheet 30, to keep top30 from spreading or otherwise changing the predetermined arrangement ofthe parts within the furnace. I heat the interior of furnace i ll bymeans of conventional heating tubes through openings in furnace wallsI2.

I claim:

1. A muffle for use under suspension within heat-treating furnacescomprising curved cast metal upper and lower corner portions, and sheetmetal side walls, top and bottom portions, said sheet portions overlyingsaid cast metal portions in broad, rounded overlaps, and welded to saidcast portions at the extreme edges of the overlapping sheet portions.

2. A mufile for use in heat-treating f-l""""" comprising a plurality ofsheet metal portions forming the side walls and top and bottom of themuffle, means to secure same comprising a plurality of rigid upper andlower corner portions welded to said sheet metal portions, a floorwithin the mufiie, and means to support same, said means comprising thelower corner portions.

3. A mufile for use under suspension within heat-treating furnacescomprising curved cast metal upper and lower corner portions and sheetsteel top, side walls and bottom portions, said sheet metal portionsbeing welded to the cast corner portions and also extending along andaround the curved portions of said bars.

4. A muffle as in claim 3 in which the upper cast steel corner portionscurve inwardly of the muifie and the sheet portions overlie said curvedcast portions.

5. A muffle as in claim 3 in which the edges of the cast portions curveaway from the sheets, and the first points of contact between sheetmetal and cast metal are removed from the edges of said cast portions.

6. A muffle as in claim 3, in which broad rounded overlaps are providedwhere the cast and sheet metal portions meet, and the welding is at theextreme edge of the overlapping sheet portion around the curve of thecorner bars.

'7. A mufile for use in heat-treating furnaces comprising a plurality ofrigid, self-sustaining cast metal portions forming the upper and lowercorner portions of the muffle, a semi-rigid sheet metal portion weldedto the upper corner portions forming the roof of the muffle, and asecond semirigid sheet metal portion welded to the lower corner portionsforming the bottom of the muffle, and a pair of semi-rigid sheet metalportions welded to the upper and lower corner portions forming the sidewalls of the muffle.

8. A mufile as in claim 7 in which the cast metal upper corners arecurved, and curve inwardly of the muffle.

9. A muffle as in claim '7, in which the cast metal corner portions arecurved, and the upper corner portions curve inwardly of the muffle, andthe lower corner portions curve inwardly and outwardly from the furnace.

10. A muffle as in claim '7 in which the cast metal lower corners have afiat central portion and curved outer edge portions.

11. A muffle as in claim '7 in which the cast metal lower corners have aflat central portion, and curved outer edge portions having reversecurvatures, one of which is within the muffle and the other of which isoutside the mufile.

12. A muille as in claim '7, with means to place the sheet metalportions forming the side walls of the muille under tension.

13. In a heat-treating furnace comprising a floor, walls and roof, amuflie comprising a pair of rigid cast metal bars forming the uppercorner portions of the muffle, a semi-rigid sheet metal portion weldedthereto forming the roof of the muffle, a second pair of rigid castmetal bars forming the lower corner portions of the muffle, a secondsemi-rigid sheet metal portion welded to said last referred to castportions forming the bottom of the muffle, a pair of semi-rigid sheetmetal portions welded to the upper and lower cast portions forming theside walls of the muiiie, and means to suspend said muffle within thefurnace to permit the weight of muffle and contents to place said lastreferred to semi-rigid sheet metal portions under tension and keep samefrom buckling.

14. A heat-treating furnace as claimed in claim 13, in which the meansto suspend said mufiie comprises ears on said cast upper corner barssecured to chains and eyebars anchored in the roof of the furnace, thechains and eyebars diverging upwardly from the muffle toward the roof.

15. In a heat-treating furnace comprising a floor, walls and roof, atmuffle comprising a pair of rigid cast metal bars forming the uppercorner portions of the muffle, a semi-rigid sheet metal portion weldedthereto forming the roof of the muffle, a second pair of rigid castmetal bars forming the lower corner portion of the muffle, a secondsemi-rigid sheet metal portion Welded to said last referred to cast barportions forming the bottom of the muffle, and means to sustain themuffle within the furnace comprising a suspending connection from theroof thereof and a supporting connection from the floor thereof.

16. In a heat-treating furnace comprising a floor, side walls and aroof, a muffle comprising a pair of rigid, self-sustaining cast metalbar portions defining the upper corners of the muflle, a sheet metalportion welded thereto forming the roof of the muffle, a second pair ofrigid selfsustaining cast metal bar portions defining the lower cornersof the muffle, and a sheet metal portion welded to said lower east barportions and forming the bottom of the muiiie, a pair of sheet metalportions welded to said upper and lower corner portions forming the sidewalls of the muffle. means to place said last referred to sheet metalportions under tension comprising a suspending connection of the mufflewithin the furnace, and a floor within the muffle supported by saidsecond referred to pair of cast metal sheet portions, the weight of thefloor and muffle contents serving to keep said side wall sheet metalportions under tension.

17. In a heat-treating furnace comprising a floor, side walls and roof,defining a chamber, a muffle maintained within said chamber, and meansto support the weight of the muffle partly from the floor of the furnaceand partly from the roof thereof.

18. In a heat treating furnace comprising a floor, side walls and aroof, a mufiie made partly of rigid metal upper and lower cornerportions, and partly of flexible sheet metal side walls top and bottomportions, means for suspending the muffle attached to the upper cornerportions and means for supporting the muffle bearing against the lowercorner portions.

19. In a heat-treating furnace comprising a floor, walls and roof, amufiie comprising cast metal upper and lower corner portions and top,bottom and side walls sheet metal portions welded to said cast corners,elevated rails within and on the floor of the furnace bearing againstthe lower east corner portions of the mufile serving to support part ofthe weight thereof, and ears on the upper cast corner portions securedto chains anchored in the roof of the furnace serving to support therest of the muflie weight.

20. A heat-treating furnace as in claim 19 in which the muffle isprovided with a plurality of cross beams serving as a bed for a floorwithin the muffle, the beams resting directly on the lower cornerportions, and the elevated rails extending longitudinally of the furnacebear directly against the underside of said lower corner portions.

21. A mufiie comprising rigid metal parts at the upper and lower cornersand flexible sheet metal roof, wall and bottom parts between and weldedto the said rigid metal parts, the bottom sheet and side sheetsrespectively being welded to opposite faces of the lower corner rigidmetal parts.

22. A muffle as in claim 21 for use under suspension within heattreating furnaces in which certain of the cast metal corner bars arecurved and curve inwardly of the mufiie and the sheet portions overliesaid curved corners and are welded thereto at the extreme edges of theoverlapping sheet portions.

HENRY H. HARRIS.

